1. Field of the Invention
This invention relates to light-emitting compounds or compositions and light-emitting devices that include the light-emitting compounds or compositions.
2. Description of the Related Art
Organic light-emitting devices (OLEDs) have been widely developed for flat panel displays, and are moving fast towards solid state lighting (SSL) applications. Organic Light Emitting Diodes (OLEDs) include a cathode, an emissive layer and an anode, and typically further include a hole transporting layer and an electron transporting layer. Light emitted from an OLED device is the result of recombination of positive charges (holes) and negative charges (electrons) inside an organic (emissive) layer. The holes and electrons combine within a single molecule or a small cluster of molecules to generate excitons, which are molecules in an excited state, or groups of organic molecules bound together in an excited state. When an exciton releases the required energy and returns to its stable state, photons are generated. The organic compound or group of compounds which forms excitons and emits photons is referred as an electro-fluorescent material or electro-phosphorescent material depending on the nature of the radiative process. Thus the OLED emissive compounds may be selected for their ability to absorb primary radiation and emit radiation of a desired wavelength. For blue emitters, for example, emission within principle emission bands of 440 to 490 nm is desirable.
Some SSL applications require white OLED devices to achieve greater than 1,500 lm brightness, a color rendering index (CRI) greater than 70, and an operating time greater than 100,000 hours at 1,000 lm/w. There are many approaches for generating white light from an OLED, but two common approaches are: direct combination of red, blue, and green light using either lateral patterning or vertical stacking of three emitters; and partial down conversion of blue light in combination with yellow phosphors. Both of these common approaches may be more effective if a highly efficient chemical- and photo-stable blue dye is employed. However, blue emitters may be less stable than dyes which emit other colors. Furthermore, there are very few blue emitting devices showing a CIE y value below about 0.2 yet while maintaining respectable efficiency. Thus, the development of deep blue emitters with good stability and high luminescence efficiency is desirable to effectively reduce power consumption and generate emission of different colors.
Certain triphenyl compounds have been used as additives in organic photoreflective polymer composites for electrooptic, photorefractive and liquid crystal applications (see for example, JP 07138568). However, none of these compounds were described as blue emitting fluorescent compounds. Thus, the development of deep blue emitters with good stability and high luminescence efficiency is desirable to effectively reduce power consumption and generate emission of different colors.